Track-laying tractor



Oct. 7, 1952- H v TUTTON 2,613,115

Y TRACK-LAYING TRACTOR Filed March 15', 1947 2 SHEETS-SHEET l INVENTOR. Harry y 7'ufon.

H. V. TUTTON TRACK-LAYING TRACTOR oct. 7, 1952 Filed Maron 15, 1947 .l l l n l I muy!!! mn. mf wf. 7M y 2 Hdl' Trax/V575,

Patented Oct. 7, 1952 UNITED STATES PATENT, OFFICE TRACK-LAYING TRACTOR Harry V. Tutton, Detroit, Mich., assigner to Sherman Products Inc., Royal' Oak, Mich.

Application March 15, 1947, Serial No. 734,946

9 Claims. l

This invention relates to track-laying tractors of the type disclosed in the copending application of Lewis'B. Merrill, Serial No. 529,087, which was led April 1, 1944 and maturedl into Patent No. 2,452,671 on the 2nd day of November, 1948.

An important object of the present invention is to provide a track-laying tractor having two or more wheels at opposite sides thereof which carry the endless tracks and wherein one of the endinost wheels at each side of the vehicle is movable longitudinally of the latter a distance sufcient to form considerable slack in the endless track associated therewith.

Another object of the invention is to provide novel means for urging said movable wheels in a direction to tauten the endless tracks so that the latter normally are stretched tightly around the wheels but wherein each movable wheel can slide longitudinally of the vehicle to provide slack in its respective track in the event the latter passes over an obstruction such as a rock, log, or stump.

Still another object of the invention is to provide a track-laying `tractor of the above-mentioned character wherein the endless tracks and their adjuncts are so constructed and arranged that the weight of the vehicle is never supported entirely by the lower runs of the tracks regardless of the type of obstruction traversed by the vehicle.

Yet another object of the invention is to provide a track-laying tractor of the above-mentioned character wherein the endless tracks tend to wrap around any obstruction traversed thereby thus relieving the tracks of excessive strain or stresses and affording additional purchase or traction for the vehicle.

A further object of the invention is to provide a novel spring system or motor for controlling the movable wheels of the tractor, which spring system is adjustable to vary the initial tension normally imposed on the endless tracks.

A still further object of the invention is to provide a novel spring system of the above-mentioned character which is uniquely constructed to afford progressively increasing resistance as the wheels move to form slack in the endless tracks.

A yet further object of the invention is to provide a spring system of the above-mentioned character wherein the initial adjustments can be made manually during operation ofthe vehicle.

Other objects and advantages of the invention will be apparent during the course of thev following description. Y

In the drawings forming a part of this specification and wherein like numerals are employed to designate like partsvthroughout the same,

` suitably fastened together (Fig. 3).

Fig. 1 is a side elevational view of a track-lay ing tractor embodying the invention,

Fig. 2 is a fragmentary, transverse sectional view taken on the line 2-2 of Fig. 1 and showing a preferred spring compensating system for` controlling the movable wheels of the vehicle,

Fig. 3 is a fragmentary, front elevational view lookingA in the direction of the arrows 3-3 in Fig. 2, I

Fig. 4 is an enlarged, fragmentary, vertical sectional view taken on the line 4--4 of Fig'. 2, and

Fig. 5 is a transverse sectional view similar to Fig. 2 but showing a modied spring compensating system.

While the essence of the present invention is embodied in the spring compensating system or motor which controls the movable wheels of the tractor, a brief description of the vehicle is rst given in order to provide a proper setting for the real invention. In this connection, however, it is to be understood that the tractor here shown is given merely by way of illustration and not by way of limitation. Except for the feature that one track-carrying wheel at each side of the vehicle must be movable longitudinally of the latter a distance suicient to form considerable slack in the tracks, the construction and operation of theA tractor may vary considerably.

The tractor here shown by way of illustration has a rigid, generally rectangular frame I0 which conveniently may be formed from any suitable type of structural member and is here shown formed of channel pieces welded or otherwise At each side of the frame I0 are front and rear track-carrying and supporting wheels I2 and I4. These wheels maybe of any suitable type or construction and are here illustrated as conventiona rubber-tired wheels.

According to the present invention one wheel in each pair must be movable for a substantial distance longitudinally of the vehicle, and the other wheel in each pair preferably is longitudinally xed. In the tractor here shown by way of illustration, the two front wheels I2 are movable longitudinally along the frame I0 and the two -'rear wheels I4 are stationary on the frame. In this connection, conventional fixed journals or mountings (not shown) are provided for the rear wheels I4, but thefront wheels I2 are carried by slides I6. The latter engage flatly at theinner sides thereof against xed guide blocks I8 which blocks are fastened solidly to and depend from the side frame members. The nat outer faces of guide blocks I8 provide solid stationary bear- 'ingfsurfaces for the slides I6 and, as lbest shown by the vehicle.

in Fig. 3, the latter are formed with horizontally projecting T-shaped guides which it snugly but slidably in correspondingly shaped guideways 22 in the guide blocks.

An endless track 24, which may be of conventional construction, is carried by each pair of wheels I2 and i4; and, when the slides I6 are positioned forwardly in the guide I8, the front wheels I2'thrust against lthe tracks 24 and hold the latter taut. However, when slides I6 occupy rearward positions in guide blocks I8 slack is formed in the endless tracks 24, as vshown by broken lines in Fig. 1.

As suggested, it is a feature of thisinvention that slides I6 have a relatively long travel so that considerable slack can be formed in endless tracks 24. For example, when the front wheels I2 move from the full to the broken line position in Fig. l, sufficient slack is formed in endless\ tracks 24 so that the latter extend over and, in effect, wrap around an obstruction 26 traversed By reason of this yunique operation, bothwheels i2 and I4 Aare available at all times toA support the Maniiestly,if the wheels I2 and I4 were longitudinally fixed or had only such slight movement as is usually provided for taking up slack inthe tracks due to natural stretching or wear, one-or vboth of the wheels I2 and I4 would be lifted-entirely off the ground by the obstruction 26; and.

when this occurred, all or a Vmajor portion of the weight .of the vehicle ywould .be .supported solely by the bottom runs 0f the tracks. This phenomenon causes frequent breakage of tracks 24 in conventional vehicles of this typebut .is obviated by the present construction. Also, by providing for considerable slackin the tracks 24, the area kof Contact between the .latter and the `obstruction 2-5 is considerably greater than if the tracks are stretched tautly between two fixed or relatively xed wheels according to conventional practice. The increased area of contact affords greater traction and thuspermits the vehicle to pass more easily over the obstruction.

The operating and control mechanism for the tractor may be conventional and .comprise no part of the present invention. An internal combustion engine 28 is here shown 'on the forward end of the frame ID, which engine drives the usual change speed transmission 30 througha conventional `type clutch, designated generally by the numeral 32. The transmission V`3I is controlled by the usual hand lever 34 and the clutch 32 is actuated bythe usual control lever 36. At the rearward Aend of the transmission is a drive shaft housing 38 which carries the usual drive shaft (not shown) and the latter drives the usual ldifferential gearing (not shown) in the housing 40. It is to be understood that the differential gearing in housing i0 has the Ausual-driving connection with the rear wheels I4,

Steering is raccomplished by braking one or the other of rear Wheels I4 and for this purpose veach rear wheel is equipped with a conventional type wheel brake mechanism designated generally by the numeral 42. In the vehicle here shown by way of illustration, each of the brakemechanisms 42 is .connected by a rod 44 to ajhand lever 4S andthe latter is supported formovement about a horizontal `pivot by a bracket 48 which is .bolted .or otherwise fastened to the frame II).

A conventional radiator 50 is mounted .on .the frame `It ahead of the engine 28 `and is connected to the latter in the conventional manner. The usual fuel tank 52 is mounted between the weight of .the vehicle.

upper end of radiator 50 and a dash structure E@ which, in turn, is supported by the frame it through the medium of suitable upright supporting members 5S. The usual seat 5:3 is provided for the operator and an instrument panel 6G carried by the dashboard structure 54 is readily accessible to the operator during operation cf the vehicle.

According to'the present invention, the mechanism for constantly urging the front wheels I2 l away from the corresponding rear wheels I4 to maintain endless tracks 24 normally in taut condition and for controlling rearward movement of the front wheelsto provide slack in the endless 'tracks when the vehicle traverses an obstruction, comprises a pair of pivoted levers 62 which are mounted on the'frame IU at opposite sides of the vehicle. The levers -62 are connected to respective slides I8 by rods 64 and to a spring motor designated generally at 6G. Means is provided for maintaining the spring motor 6G normally under tension and the arrangement is such that the latter acts simultaneously on both slides it throughthe medium of levers 52 and links 62 to maintain a constant forward pressure against the front wheels I2. As a result, the endless tracks 2.4i normally `are taut; but, if the vehicle passes @veran obstruction 26 which ordinarily Awould leave one or both ofthe wheels I2 or Ill temporarily on .the ground, the slides I6 are ire-e to move rearwardly against lthe resilient action of the spring motor 66 and thus prevent excessive or destructive stresses from being Vdeveloped in the tracks.

In practice,.it has been found desirable to adjust .the .tension normally maintained on the tracks24 .according to the terrain being traversed .at the time. With this end in view, the spring motor e6 preferably is equipped with a l.manually operated device, designated generally at G8, for Aadjusting the preload tension of the spring motor and the device 68 is actuated b/ suitable control means 'i0 and i2 on the instrunient panel BIJ through .the medium of Bowden or similar type control cables I4 and 16.

.In the form of theinvention shown in Figs. 2-4, the levers E2 are in the form of triangular plates, which plates are fastened at one corner thereof to the frame I0 by pivots 'I'I and brackets 13. As bestshown in' Fig; 3, the levers 62 are disposed entirely below the frame I0 and a second corner thereof` projects laterally of the frame to connect with .rods 6A. The third or remaining corners of levers 62 are pivotally attached to opposite ends of the spring motor 5S.'

Broadly, the spring motor 66 may be any type interposed between the two levers 52; however, in order `that Yresistance to rearward movement of frontwheels I2 .may be maintained properly and increased progressively without overloading the control springs, the construction shown in the drawing and particularly `in Fig. 4 is preferred. This construction comprises a free-floating rodlike supporting .member which carries two series .of 4compression springs at opposite ends thereof. Each ,series is here shown as comprising three separatefsprings 84, and 83, which springs increaseprogressively in size and strength ,fromone end of the series to the other, are arranged in end-to-end relation and separated by suitable spacers 90. One series of springs is shown in detail in Fig. 4.y End plates 92 also are providedat opposite ends of the series for conning the respective springs 84, 86 and B8.

Spacers 90 and end plates 92 snugly t the support 80 and preferably are formed with annular peripheral recesses 94 which seat the ends of the springs and hold the same generally concentric to the support. In order to hold the springs under tension the inner end plates92v are stationary on support 80;however, the spacers 90 and the outermost end plates 92 are freely slidable on the support. Also, it will be observed that the outermost end plates are provided with integral brackets 96 which are fastened to the levers 62 by pivots 08. Spacers 00 and end plates 82 carry rotatably fixed but mutually telescoping casings |00 which surround and shield the springs 84, 86 and 88; and the end plates additionally are equipped with bellows-type seals |02 which accommodate the projecting portions of the support 80 and prevent dirt from gaining access into the casings |00. f i

As a result of the above construction and arrangement of parts, the front wheels `I2 are moved rearwardly by endless tracks24 when the vehicle traverses an obstruction 26. Rearward movement of Vthe Wheels I2 rocksvlevers 62- about pivots 11 and acts through the outer end plates 92 to compress springs 84, 86 and 88. Manifestly, since both the outer end plates 92 and the spacers 80 are `freely slidable on the support 80, the load imposed on the spring motor 66 is taken rst by the two smallest springs 84; and, as the load on the motor increases, the loadis progressively taken up by the larger springs .80 and 88. In this manner, resistance to movement of the Wheels I2 increases gradually as the load increases and possibility of overloading of any spring in the system is reduced to a minimum.

As the rear Wheels I4 move onto the obstruction 26 and the weight of the vehicle is removed from the lower runs of tracks 2 4 the spring motor 66 gradually advances the front Wheelssand maintains the endless tracks 24 substantially uniformly taut at all times.

Manifestly, the operation is the same regardless whether the front wheels I 2 are retracted individually or concomitantly. If onlyone track 24 passes over an obstruction, such as 'a rock or stump, only the front wheel I2 associated with such track is retracted and the loadis transmitted to the spring motor 66 fromonlyone end thereof. In this connection, however, itv will vbe noted that the entire spring motor 66 including support 80 is `mounted for free movement trans'- versely of the vehicle; consequently, as the front wheel I2 is retracted, the load is transmitted simultaneously to both series of springs in the motor 66. Thus, the load is distributed substantially equally between the two sets of springs and the latter operate in unison to control movement of the single wheel I2. On the other hand,` if the two tracks 24 simultaneously encounter an obstruction, such as a log or the like, which retracts both front wheels I2 in unison and imposes a load on the spring motor 66 substantially simultaneously from both ends thereof, all of the springs in the motor are equally available to assume the load and to control the front wheels I2. Thus, the device operates in'substantially the same manner regardless of whether'the wheels I2 are retracted individually or in unison or whether they are retractedequal distances or at the same rate. l

As suggested, it is desirable thoughA not essential that means be provided for adjusting the initial tension or preload normally maintained on springs 84, 86 and 88 and that this means be 6 adapted to regulate the tension while the vehicle is being operated. According to the present invention, this operation is performed by the device 68 which comprises threaded connections I0 I between support 80 and the inner plates 82, a

worm gear |04 loosely mounted on the support between such threaded connections, a worin |06 for driving the worm gear and a, clutch |08 for selectively attaching the worm gear to the support. The worm gear |04, worm |06 and clutch |08 are all enclosed in a housing ||0 and the latter is equipped with suitable bushings ||2 which snugly but rotatably receive the support 80. Spacers I I4 at opposite sides of the worm gear |04 hold the latter from the internal walls of the housing ||0 and in proper mesh with the worm |06. Also, it will be observed that the housing I0 is formed with hubs IB which extend axially along the support 80 and carry the inner ends of the adjacent bellows seals |02, whereby the latter keep dirt and the like from the gearing and other mechanism in the housing. Manifestly, if clutch |08 is engaged with gear |04, rotation imparted thereto by worm |06 is transmitted to support 80, and rotation of the latter moves the inner plates 92 axially along the threaded portions I0 I. Thus, the tension on springs 84, 86, and 88 is increased or reduced depending on which way the support 80.is rotated. Also, it vwill be readilyapparent that the energy normally stored in the springs 84, 86 and 88 can be released substantially instantaneously by disengaging the clutch 08 from the worm gear |04. j

The flexible control cable I4 is adapted for rotatably driving the worm |06, and the manual control 'I0 for the cable preferably is in the form of a small crank,` as best shown inFig. 1. The flexible control cable 'I6 sadapted to transmit axial or longitudinal movement and it is connected to the clutch |08 by a bell crank lever I8. Clutch |08 is held normally retracted or disengaged from Worm gear |04 by a spring |20, and manual control I2 for the cable 'I6 is in the form of a small push button@ Thus, the operator can engage or disengage the clutch |08 merely by pushing or pulling the `control member '12.

In operation of the mechanism for selectively preloading the spring motor 66, support is rotated either to the right or to the left by engaging the clutch |08 and manually actuating the control 10. As the support 80 rotates, the inner end plates 92 advance or retract on the threaded portions IOI depending on which direction support 80 is rotated; and, since the outer end plates 92 are held relatively stationary by levers 62, such movement of the inner plates changes the distance between the end plates and thus varies the preload tension on springs 84, 86, and 88. Also, it will be readily apparent that the preload tension imposed on the springs can be regulated by the operator during actual operation of the tractor.

The. form of the invention shown in Fig. 5 is identical to the form hereinabove described except that the spring motor 66 is equipped with only a single series of springs 84, 86 and 88 and is mounted so that the single spring system controls both of the front wheel slides I6. In this form of the invention, the housing II@ is pivoted at |22 to a front transverse member of the frame I0 and suiiicient clearance is provided between the housing and the frame so that the motor can rock back and forth about the pivot |22. The bracket 9S at the distal or swinging end of the spring motor is pivoted substantially 7 midway .between the Aends .of a 'lever il 24, .fand the ends .of the latter `arepivoted to respective 'levers 62 vby connecting rods 11:24. In this `form of the invention 'levers lB2 :preferably vfare :in :the .form of straight `bars `which .are `pivoted 'at substantially the .middle .thereof `to lbrackets 1-8.

In operation lthe latter forrn .of .the .invention is .quite `similar to .the .form first described. .If both iront wheels 112 iretrac't 'in zunison, the spring motor yB6 is compressed by #forces transmitted simultaneously .against both ends .of 'lever 124. As the vehicle passes over "the log .or other fobstruction causing-.retraction :of the wheels I2, Ithe spring motor '66 expands to yadvance 4the Wheels to their initial Yposition exactly "in the manner described in connection `'with the fil-rst form Iof the invention. On the other hand, if only one front wheel |12 is retracted, the'lever 62 and rod associated -with `such ywheel Aacts 'against the lever H24 to-compress the 'springmotor'66; while,

the lever-62 androd |26 associated-With the other front vwheel I2 remains stationary. `In order ito compensate lfor movement ofthe first-mentioned lever `62 Yand rod |26,'the`housing .Ilrocks about pivot |22 vand thus adjusts or compensates .automatically to the `pullof .the retracting wheel I2. Also, the spring motor `66 'automatically rights itself and vreturns 'the retracted wheel l2 to its initial or -advanced. lposition when the vehicle passes over the obstruction.

It is to be understood that the forms of kthe invention herewith shown and described are to be taken as preferred examples of the same and that various changes .in the size, shape and arrangement of parts may .be .resorted to without departing from the spirit of the invention or the scope of the appended claims.

Having thus described the invention, I claim:

l. In a tractor vehicle, a pair -of vehicle supporting wheels at each side of -thevvehicle, an endless track .trained vover .and Yaround each pair of wheels with .its Alower run unsupported `between said wheels, a mounting for one wheel in .each pair permitting bodily movement thereof longitudinally of said vehicle and relative to the-other wheel with which itis associated, mechanism for urging said .movable wheels constantly -away from the other -of said wheels, said mechanism including levers ,pivoted on the vehicle and connested to said movable wheel vmountings in such manner as yto be rocked about said pivots by movement of said mountings in a .direction to ioosen endless belts, .spring means oonned v said levers and acted upon simultaneously by the latter to yieldably resist :movement by said mountings in said mentioned direction, said spring means exerting less force 'tending to separate the wheels on Aeach 'side of said vehicle than that force required to support either side of said vehicle solely through engagement of the unsupported lower run portion of the track on the side of said v'vehicle with an object over which said lower run travels, means for imposing a preload tension on `said spring means including arotatableshaft having a screw-threaded connection with the spring means, `whereby at vleast one .end of said spring means moves axially on the shaft when the .latteris rotated, a driven worm gear loosely mounted on the shaft, a driving worm .in mesh with said worm gear, clutch means .rotatablyxed but slidable on said shaft and engageable with the worm `gearto `lock the same for rotation with the shaft, and separate means ,for manually actuating said worm and saidiclutchmeans.

Z2. .In a tractor ivehiola a pair of vehicle Asupporting wheels :at `each side of the vehicle, :an .endless track .trained 4overand around each pair of wheels withlits :lower run unsupported between lsaid wheels., 1.a mounting for one wheel in each :pair 'permitting vbodily .movement thereof longitudinally of .said vehicle and vrelative to the other wheel with which 'it vis associated, mechanism for urging said movable wheels constantly away from the .other Vof said wheels land in a direction .to tauten said endless tracks, said mechanism including V'levers pivoted .on .the vehicle and connected f-tosaidmovable wheel mountings in such manner as ito be rocked about said pivots 'by movement Aof `the Lmountings, spring means for controlling each of said mountings, said spring means arranged transversely of the vehicle, fastened l'at rtheouter-ends thereof to said levers and operative `to resist movement of said wheel mountings in a direction to form slack in said endless tracks, l'said spring means exerting less force tending to separate the wheels on each side of 'said vehicle than that force required to support either side of 'said vehicle solely through engagement of lthe unsupported lower run portion of the track on the 'same side of said vehicle with an object over which said ylower run travels yand support means for vthe inner ends of said spring means.

r3. The combination as 'set forth in lclaim 2 wherein a single support is provided for both of said spring vmeans and wherein the support is mounted to vmove freely transversely of the vehicle.

4. In a tractor vehicle, a pair of vehicle supporting wheels .at each side of the vehicle, and endless track 'trained over and around each pair of `wheels vwith'its'low-er run unsupported between said wheels, a mounting for one wheel in each pair permitting bodily .movement thereof longitudinally of said vehicle-and'relative to the other wheel with which it is associated, mechanism .for urging said movable wheels constantly away from vthe other of said wheels, said mechanism including levers lpivoted on the vehicle and con- .nected to said movable wheel mountings in such manner as to be rocked about said pivots by movement of said mountings, .a support means arranged transversely .of said .levers free to move transversely ofthe vehicle, and a separate .spring meansior each lever carried by said support, the outer ends 'of said spring means confined by their respective 'levers andthe inner ends thereof fastened to .said support means, said spring means exerting less force tending to separate the -wheels on each side of said vehicle than that force re- .quired to .support either side .of said vehicle solely through engagement of the unsupported lower run portion of the track on vthe same side of said Vehicle with an object Aover which said vlower run travels.

5. In -a .tractor vehicle, a pair of vehicle supporting wheels at .each side of the vehicley an .endless track trained over and around each pair of wheels with its lower run unsupported between .said wheels, a mounting for one wheel in each .pair permitting bodily movement thereof longitudinally of said vehicle and relative to the other wheel with which it is associated, mechanism .for urging said movable wheels constantly away from the other of said wheels, said mechanism `including levers pivoted on the vehicle and connected to said movable zwh'eel mountings in such manner fas to V*be rocked :1 ab'outsaid pivots by movement of said mountings-,a .supportmeans arranged intermediate. said levers and free to move transversely of the ,vehicle,- a separate spring means for each lever carriedby said support, theouter ends ,orsaidspringmeans confined by their respectiverzlevers,andv the inner ends thereof fastenedvto Vsaidv'support means, said spring means exerting less forcextending to separate the wheels .oneachjside of said vehicle than that force required to support either side of said vehicle solely throughengagement of the unsupported lower runV portion of the track on the same side of said vehicle with an object over which said lower run travels, andmeans for adjusting the inner ends of said spring means relative tothe confined outer ends thereof toimpose a selected preload tension thereon.

6. In a tractor vehicle, a Vpant-of vehiclevsupporting wheels at each -sidef-o'fvthe vehicle, an endless track trained over and around each pair of wheels with its lower run unsupported between said wheels, a mounting for one wheel in each pair permitting bodily movement thereof longitudinally of said vehicle and relative to the other wheel with which it is associated, mechanism `for urging said movable Wheels constantly away from the other of said wheels and in a direction to tauten said endless belts, said mechanism including levers pivoted on the vehicle and con nected to said movable wheel mountings in such manner as to be rocked about said pivots by movement of said mountings, resilient means arranged transversely of the vehicle, a separate resilient means provided for each lever and each resilient means confined at one end by its respective lever, and support means mounted for unrestricted movement transversely of the vehicle frame and confining the other endsA of said resilient means, each of said resilient means consisting of separate spring elements so constructed and arranged as to operate progressively when load is imposed thereon, whereby said resilient means yieldably resist movement of said mountings in a direction to permit slack to form in said endless tracks and whereby resistancel aiorded by said resilient means to movement of the mountingsbecomes progressively greater as the load imposed thereon increases, and resilient means exerting less force tending to separate the wheels on each side of said vehicle than that force required to support either side of said vehicle solely through engagement of the unsupported lower run portion of the track on the same side of said vehicle with an object over which said lower run travels.

'7. In a tractor vehicle, a pair of vehicle supporting wheels at each side of the vehicle, an endless track trained over and around each pair of wheels with its lower run unsupported between said wheels, a mounting for one wheel in each pair permitting bodily movement thereof longitudinally of said vehicle relative to the other wheel with which it is associated, mechanism for urging said movable wheels constantly away from the other of said wheels and in -a direction to tauten said endless belts, said mechanism including levers pivoted on the vehicle and connected to said movable wheel mountings in such manner as to be rocked about said pivots by movement of said mountings, resilient means arranged transversely of the vehicle, a separate resilient means being provided for each lever 4and each ,i resilient means being fa,stened,f atjits outerend to its respective lever, means :providing acommon support for the innerendsof said resilientmeans and mounted for unrestricted'movement transversely of the vehicleframe,` saidffsupportbeing fastened attthe innerends o-fsaid` resilient means andholding` said inner, ends in iixedv relation, each of saidl resilient means including-a plurality of v, spring `elements disposed transversely `of the've# hicle, said spring elements. ,arrangedyin'end-tovend relation v-and of lprogressively lincreasing size,-

and spacers separating said springielements slide, ably mounted on Saidsupport means, said'resil-l ient means exerting lessforce-tending to separate thefwheels on each side of thevehicle thanthat each pair permitting bodily movement thereof longitudinally of said vehicle and. relative to the other wheel with which it is associated, mechanism for urging said movable wheelsconstantly away from the other of said wheels, said mechanism including a pair of pivoted levers at opposite sides of the vehicle connected to respective wheel mountings in such manner as to be rocked about said pivots by movement of said mountings in a direction to form slack in said endless tracks, a rodlike element pivoted to the vehicle intermediate said levers, spring means around and fastened at one end to said rodlike element and movable therewith about said pivot, said spring means` comprising a plurality of separate spring elements arranged in end-to-end relation and increasing progressively in size and strength from one end of the series to the other, spacers separating ycertain spring elements slidably mounted on said rodlike element, a rocker arm fastened to the other end of said spring means,

and links connecting the ends of said rocker arm to respective levers, whereby a single spring means is operative to control both of said levers y Vand to yieldably resist independent or simultaneous movement of said wheel mountings in a direction to form slack in said endless tracks, said spring means exerting less force tending to separate the wheels on each side of said vehicle than that force required to support either side of said vehicle solely through engagement of the unsup ported lower run portion of the track on the same side of said vehicle with an object over which said lower run travels.

9. In a tractor vehicle, a pair of vehicle supporting wheels at each side of the vehicle, an endless track trained over and around each pair of wheels with its'lower run unsupported between said wheels, a mounting for one wheel in each pair permitting bodily movement thereof longitudinally of said vehicle and relative to the other wheel with which it is associated, mechanism for urging said movable wheels constantly away from the other of said wheels, said mechanism including a pair of pivoted levers at opposite sides of the vehicle connected to respective wheel mountings in such manner as to be rocked about said pivots by movement of said mountings in a direction to form slack in said endless tracks,

- 11` meansv controlliislg'v 'movement of :said levers .including a. rodlifkeelement -pivoted to'fthe vehicle intermediate :saidlevers, spring means around andfastened 'at lone end to said rodlike element and 4-xnvable "therewith about said pivots, a ro cker arm .fastened to 'theother end of said spring means, fand links'. connecting the ends of said rocker arm to respective levers, said spring means comprising ae 'plurality of Aseparate spring elements arranged Ain fseries vrelation and increasing progressively .in 'size 'and strength from one end ofl the series 'to the other, and spacers separating saids'pring elements, the vendm'ost spacer adjacent the .pivot `about which the rodlik'e element 'swings normally being fixed to but :longitudinally adjustable on .said rodlike element, the other of saldspacers being 'slidable on the .rodli-ke element and .endmostfspacertremote from the pivot .about which'ithe ro'dllke felement swings .being fastened to said rocker arm, whereby a single .springmeans is operative to control both 'of said .levers and REFERENCES :CIT-ED The l'following references are foi' record in the 15 file of this patent: I'

'UNITED STATES PATENTS Number NameA Date 1,429,589 Helm l fSept. 19, .1922 2o 1,800,221 Knox ,Apr.14,193l 2;452,67l .Merrill Nov. 2, 1948 

